1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member having a photosensitive layer containing a crystalline charge-generating material.
2. Related Background Art
Hitherto widely used as electrophotographic photosensitive members comprising an inorganic photoconductive material have been those employing selenium, cadmium sulfide, zinc sulfide or the like.
On the other hand, known electrophotographic photosensitive members comprising an organic photoconductive material are those employing photoconductive polymers as typified by poly-N-vinyl carbazole or low molecular organic photoconductive materials such as 2,5-bis(p-diethylaminophenyl)-1,2,3-oxadiazole, and also those comprising the combination of such organic photoconductive materials with all sorts of dyes or pigments.
The electrophotographic photosensitive members employing the organic photoconductive materials have the advantage that they can be produced by coating, can achieve a very high productivity, and can provide inexpensive photosensitive members. They also have the advantages such that the color-sensitivity can be arbitrarily controlled by appropriately selecting dyes or pigments to be used or sensitizers therefor, and thus have been studied over a wide range. Particularly, in recent years, a functionally separated photosensitive member comprising a charge generation layer comprised of an organic photoconductive pigment, laminated with the so-called charge transport layer comprised of the above-mentioned photoconductive polymer or low molecular organic photoconductive material, has been developed to bring about remarkable improvement in the sensitivity and durability in which the conventional organic electrophotographic photosensitive members have been regarded as defective, and has come to be put into practical use. Various compounds and pigments suitable for the functionally separated photosensitive member have also been discovered.
In such a functionally separated electrophotographic photosensitive member, a number of organic dyes or organic pigments are proposed in, for example, U.S. Pat. No. 4,356,246, U.S. Pat. No. 4,551,404, U.S. Pat. No. 4,571,369, U.S. Pat. No. 4,582,771, Patent Laid Open application No. 61-228453 and Patent Laid Open application No. 61-275850, as charged-generating materials therefor.
However, they can not necessarily be satisfactory for the sensitivity and the potential characteristics such as residual potential and stability in repeated use.
In recent years, with the spread of computers, there also developed progressively printers or copying machines in which semiconductor lasers, LED or the like are used as exposure light sources. Sought after as photosensitive members used in these are photosensitive members having a high sensitivity to near infrared light. The fact, however, it that those having a high sensitivity to near infrared region (particularly 750 nm or more) are only sparingly available among the organic dyes or organic pigments.
In instances where such organic dyes or organic pigments are used as charge-generating materials, the electrophotographic characteristics are known to be greatly affected by crystal forms including the non-crystalline form. For example, Patent Laid Open application No. 56-116038 discloses that crystalline bisazo pigments have sensitivity about 5 times greater as compared with that of non-crystalline ones. Patent Laid Open application No. 59-81647 also discloses that a non-crystalline bisazo pigment such that in a powder diffraction pattern the maximum value of the diffraction intensity at 2.theta.=26.degree. to 2.theta.=28.degree. on the basis of the diffraction intensity at 2.theta.=35.degree. is smaller than 3 times the average value of the diffraction intensity at 2.theta.=18.degree. to 2.theta.=22.degree. on the basis of the diffraction intensity at 2.theta.=35.degree. has a high sensitivity. Patent Laid Open application No. 51-108847 also discloses that a copper phthalocyanine pigment having a particular crystal form among a number of crystal forms of copper phthalocyanines can be an effective component of an electrophotographic photosensitive member. Thus, some report that crystalline materials have a higher sensitivity than non-crystalline materials depending on the types of organic dyes or organic pigments and on the contrary some report that non-crystalline materials have a higher sensitivity than crystalline materials. Accordingly, it has been considered difficult to predict how the crystal forms of the respective organic dyes or organic pigments affect the electrophotographic characteristics.